This invention relates to item tracking systems and inventory management and more particularly to an antenna assembly for use with an RFID tracking system.
“Smart shelves” refer to systems used to identify articles equipped with a radio frequency identification (RFID) transponder, or “tag”. Smart shelf systems are capable of determining the number, identity, and location of RFID tagged items placed on a store shelf, book shelf, or in a cabinet. When these shelves or other fixtures are equipped with one or more antennas coupled to an RFID interrogator, the contents of an article's tag may be read by the RFID interrogator. The number and location of each article may then be obtained and the location and use of the article tracked. Out of stock situations may be avoided and reordering of articles may also be handled automatically based upon information from the system.
RFID antenna systems for use with shelf systems have unique design specifications. Antenna systems must be designed to obtain information from RFID tags within a limited area. The antenna systems should not read RFID tags from adjacent shelves.
Because an RFID antenna system within a shelf is to be effective within a relatively small area, traditional “far field” analysis of the antenna systems is not useful. Rather, coverage by the RFID antenna with the “near field” of approximately zero to sixteen inches from the antenna system must be optimized.
As is well known, antennas have dead zones, referred to generally as nulls. Objects placed in a null of an antenna will not couple with the antenna. If complete coverage for an area is required, multiple antennas must be used. Multiple antennas, however, present an additional problem. Antennas in close proximity couple, thereby creating additional nulls. This is especially problematic in the near field since the coupling between the antennas can be particularly strong.
One use of smart shelves is to track medical supplies having RFID tags. Some medical supplies are extremely expensive, costing several thousand dollars per item. The medical supplies are often used at the medical facility, and their use may be billed to a particular patient. Thus, maintaining an accurate inventory and location of expensive medical supplies is important.
Medical RFID systems previously proposed are expensive, involving elaborate storage containers made specifically for scanning RFID equipped articles. The containers cannot be easily adjusted to accommodate different size articles. Additionally, the RFID systems are not easily moved from one location to another. Further, the accuracy of current RFID systems for use in medical facilities is less than desirable.
Thus, an improved antenna system for tracking articles stored within a cabinet or shelving system is highly desirable.